The invention relates to an apparatus for ultrasonic wire bonding, whereby contact locations can be joined by ultrasonic welding and wire straps, e.g. connections from component mounts or the like to the bonding islands of semiconductor chips.
With known apparatuses for ultrasonic wire bonding, as a rule the wire is fed through an inclined bore in the longitudinal direction of the ultrasonic generator, which bore is disposed behind the welding surface of a sonotrode. This customary arrangement requires that prior to the fixing of each wire strap the connecting orientations at the two connecting loci of the strap must be aligned with the axial direction of the ultrasound generator.
For this purpose, either the component mount or a bonding head which includes the ultrasound generator must be aligned in the required direction. When automatic apparatus is used for certain areas of application, e.g. for operations on so-called hybrid components, it is advantageous to proceed by adjusting the bonding head. Known apparatuses of this type have a bonding head which is rotatable around a vertical axis which axis approximately passes through the welding surface at the foot of the sonotrode, wherewith the bonding head as a rule is also movable vertically. In addition, all known embodiments have an optical device disposed near the axis of rotation, whereby the component being operated on can be depicted on a monitor by means of a television camera.
In a device well known in practice (described in U.S. Pat. No. 4,239,144), a hollow shaft is provided which is disposed on two radial bearings, for radial guiding of the bonding head, which shaft has a downwardly directed fixed connecting member. A carriage is mounted on this fixed connecting member, which carriage is vertically movable in ball bearings and which bears the bonding head proper. A bar mounted in the rotational pivot is provided, for coupling the carriage to the vertical drive means. Said bar passes through the center bore of a rod which is fixed to the machine frame and which extends into the hollow shaft from above. This rod further has an eccentrically disposed bore, in the bottom of which a lens system is mounted which serves an an objective.
A disadvantage of this arrangement is that the axis of the objective is at a relatively large lateral distance from the rotational axis. Therefore the movement path between the viewing position and bonding position (for any given bonding position and given viewing position) for the connecting points of the component is substantial. Also, the diameters of the radial bearings are relatively large, so that the structure has a large moment of inertia, and the lens system must have a relatively small diameter, rendering impossible the use of a normal objective.
Also well known in practice is a device wherein the bonding head is fixedly mounted on a subassembly comprised of the radial guide means and the drive means for the rotational movement. This subassembly is attached to a vertically guided carriage which executes the vertical movement. A disadvantage of this arrangement is particularly that the mass which must be moved vertically is high, thereby limiting the possible speed of operation.